1. Field of the Invention
The present invention relates to a method of manufacturing an aluminum heat exchanger, and more particularly it relates to a method of manufacturing a heat exchanger made of aluminum and having pipes and their support plates brazed with a high degree of rigidity and fluid-tighteness.
2. Prior Art
Recent aluminum heat exchangers for use as radiators on automobiles include brazing sheets comprising an aluminum alloy core clad on one or both sides with an aluminum brazing filler alloy containing silicon, magnesium and similar materials and having a melting point lower than that of the core. The brazing sheets are formed into pipes, support plates and fins which are then assembled and held together by a jig. The assembly is put into a furnace wherein it is heated up to a temperature at which the brazing filler metal is melted, but the core is not melted, whereupon the melted filler metal is distributed into the joints. The assembly is then removed from the furnace and cooled, to thereby provide a brazed heat exchanger. Usually, it is sufficient to use a filler-clad member as one of two parts to be joined.
A problem with prior brazing processes is that melted filler metal may not come to where it should be, with the result that a completed exchanger may suffer from water leakage. For example, FIG. 1 shows a portion of a conventional heat exchanger 10 having a support plate 11 including an aluminum core 12 clad on upper and lower surfaces with a pair of brazing filler layers 13 and 14, respectively, and a non-clad water pipe 15 extending through an aperture 16 in the support plate 11. The filler layer 13; when melted, wets the joint between the support plate 11 and the water pipe 15 by surface tension. However, the melted layer is not sufficient in volume to provide a rigid connection. The melted filler layer 14 is also attracted to the joint on account of surface tension, but is liable to flow down along the outer wall of the water pipe 15.
According to another prior proposal illustrated in FIG. 2, an edge bounding an aperture 26 in a support plate 21 is upturned for facilitating the insertion of a water pipe 25 into the plate 21. With this structure, however, melted filler metal flows away from the joint and cannot provide rigid brazing.
A still another prior attempt is shown in FIG. 3 in which an edge that defines a pipe-receiving aperture 36 is bent uprightly so that a lower filler layer 34 is held in contact with the outer wall of a water pipe 35. When the filler layer 34 is melted, it flows down, leaving a gap between a core 32 of a support plate 31 and the water pipe 35 only by action of surface tension. Water leakage is then apt to occur through the gap.